This invention relates to an image detection and magnification system and particularly, but not exclusively, to a low vision rehabilitation system.
Low vision rehabilitation systems are commonly used to provide assistance to visually impaired persons, particularly to individuals whose vision in either or both eyes has been impaired as a result of retinal damage. Such a system presents the user with a magnified image of a scene. Although the damaged portion of the user""s retina cannot adequately detect portions of the magnified image, it has been found that a user can more easily see features using the still functional portions of his or her retina as a result of the magnification.
There are some purely optical low vision rehabilitation systems which are mounted on a headset to be worn by the user. Other types of system use a video camera and display, also mounted in a headset. This latter type of system can provide a brighter image than a purely optical system, and can also be equipped with a facility for image enhancement (by, for example, increasing contrast between light and dark areas of an image), which can be particularly useful for activities such as reading. However, the camera based systems tend to be cumbersome, and obtrusive.
This is partly because the camera needs to be able to provide a path for light through the camera""s magnifying lens system and onto its transducer (e.g. a CCD chip) which is sufficiently long to enable the desired magnification to be achieved.
According to a first aspect of the invention, there is provided an image magnification and display system comprising a camera for generating an electrical output signal representative of the detected image, the camera being carried by a headset for attachment to the head of a user, the camera comprising a transducer means for generating an electrical output in response to light incident thereon and magnifying means, situated in the path of light to the transducer means, the transducer means and magnifying means being positioned such that, in use, the portion of the path of light passing through the magnifying means extends laterally across the front of the user""s head.
Thus, in use, the camera is accommodated across the front of the user""s face, which is a far more compact arrangement than at least some known camera based systems in which said path extends from the front towards the rear of the user""s head, and the camera as a result has to be mounted on top of the headset or has to have a barrel which projects forwards from the headset. Consequently the system according to the present invention can be made more attractive than such known arrangements. Furthermore, the system exerts a smaller moment on the headset than is the case with a known arrangement with top mounted or forward projecting camera barrels, and therefore has a lower apparent weight than known systems.
Preferably, with the headset mounted on the head of a user, the portion of said path extends horizontally across the user""s face, preferably from one side of the user""s nose to the other.
To that end, the camera may to advantage further comprise an elongate housing having at one end region an entrance for incident light, the transducer means being situated in the region of the opposite end of the housing, the magnification means being interposed between the entrance and the transducer means.
Conveniently, the transducer means comprises a CCD chip. Preferably, the entrance is situated in a forward facing portion of the housing, and the camera includes a reflector for reflecting light, incident in a direction perpendicular to the housing axis, along said axis.
Preferably, the transducer means has a light sensitive surface on which an image to be displayed is formed and which is substantially perpendicular to the housing axis.
The housing may to advantage be rotatably mounted on the headgear so as to be rotatable about its own axis, the transducer means being so positioned as to receive light from the magnifying means at any angular position of the housing (relative to its axis).
To that end, the transducer means is preferably either mounted in a fixed angular position on or in the housing so as to rotate therewith, and/or is mounted in a position in which it intersects the housing axis.
This enables the user to change the field of view of the camera simply by rotating the housing.
The housing may be between 25 and 50 mm long and preferably is of a length of not more than 40 mm.
Preferably, the magnifying means forms part of a focusing device for enabling the camera to obtain focused images of objects at varying distances therefrom, the focusing means being linked to the housing in such a way that rotation of the latter adjusts the focusing means.
Preferably, the focusing means is arranged so that rotation of the camera so as to lower the field of view enables the camera to focus on proximate objects whilst rotating the housing to raise the field of view enables focused images of distant objects to be obtained.
Such focusing means may comprise a lens which is mounted in the housing and is so connected to the housing as to be moved therealong by rotation of the housing about its axis.
According to a second aspect of the invention, there is provided an image detection system comprising a camera for detecting an image from a viewing direction, the attitude of the camera being adjustable to alter the elevation of the viewing direction, the camera having focusing means adjustable to enable to system to switch between a far focus mode, in which the camera focuses on distant objects, and a near focus mode, in which it focuses on proximate objects, wherein the system includes linkage means operatively linking the focusing means to the camera attitude so that the tilting of the viewing direction downwards causes the system to change from the far to the near focus mode.
Normally, when a person is looking into the far distance, they tend to look upwards by about 10xc2x0, whereas if they wish to read something (i.e. to focus on an object at a close distance), they tilt their eyes downwards by about 40xc2x0. If the change of attitude of the camera is used to mimic this change, the system of the invention will automatically refocus to enable the camera to view close objects, thus making the system particularly useful as a visual aid, for example a low visual rehabilitation system, to be worn by the user.
Preferably, the camera and display means are mounted on a headset to be worn by the user, at least part of the camera being movably mounted on the headset to enable the elevation of the viewing direction to be altered, the system being in the near focus mode at the lowest elevation of the viewing direction.
Preferably, the linkage means comprises a mechanical link between the camera and the headset, and the focusing means comprises lens means (for example a single lens or a system of lenses) in the camera, wherein said movement of the camera causes the linkage means to move the lens means relative to an image sensor in the camera.
Preferably, the linkage means causes a progressive adjustment of the focusing means between the two modes, in response to changes in the attitude of the camera.
Preferably, the camera comprises a cylindrical body, in which the focusing means is situated between the sensor means and a viewing port in the side of the body, wherein the camera includes at least one mirror for reflecting light, which has entered the viewing port, along the body to the sensor.
Conveniently, the body is rotatably mounted on a headset for rotation about its axis to change the elevation of said viewing directions.
Preferably, in this case, the mechanical linkage comprises a protuberance which engages in a part-helical guide, wherein rotation of the camera causes relative rotation of the protuberance and part helical guide about the axis of rotation of the camera, and wherein the protuberance engages or is attached to the lens means so that said rotation moves the lens means axially along the camera.
Preferably, the protuberance comprises a pin attached to a holder of the lens system, and the guide comprises a part-helical slot in the camera body, the pin extending through the slot and into a further guide which is fixed relative to the headset, and which extends in the direction of the body axis, thereby to provide angular location of the lens means relative to the camera body.
Preferably, when it is in near focus mode, the camera has a focus distance of approximately 240 mm with a near limit of depth of field of approximately 100 mm, and preferably has a hyper focal distance of approximately 4 m, with a far limit depth of field of 2 m infinity, when in its far focus mode.
Conveniently, the camera body is mounted transversely across the front of the head set.
Preferably, the system comprises a low vision rehabilitation system.